Choosing a meditation focus

I have meditated daily for a few years now, mainly just focusing on having a clear mind and on my breathing.

Recently though I have been using my meditation to practice inducing lucid dreams i.e. walking down some steps, gradually getting deeper into a trance, focusing on the smells and feelings, so that will find this easier to do in WBTB.

I have also read one can meditate on positive affirmations (something I have considered doing to tackle negative thoughts).

I never know which to focus on and can end up not focused at all. I've considered focusing on one thing per day, but any thoughts would be welcome!

My buddy used a really nice technique where he run would through a forest and slowly try to visualize him getting more exhausted as he went. When he was almost at the threshold he would find a cave enter it and jump down into the lowest levels via a shaft. He would enter the dream falling and then immediately the cave bottom would surround him.

I like the idea of focusing on one per day. You can even dedicate certain days to certain things, if you like. For example, your Fridays could be "combating negative thoughts" days, whereas your Tuesdays could be "lucidity" days. So on and so forth.